The present invention relates to an electrostatic image recording machine such as a plain paper copier or a printer, and an electrostatic image recording method.
When an original including both a letter text part and a photograph part (such as a page of newspaper) is copied by an electrostatic copying machine, it is difficult to obtain an exact reproduction of the original for the both parts. When the text part is intended to be reproduced correctly, the .gamma.-value (the slope of the characteristic curve relating the density of the copy image to that of the original) should be large in order to obtain a crisp (i.e., high gradation) image with a clear background. When the photograph part is intended to be reproduced correctly, the .gamma.-value should be near the unity (1) to obtain a gentle (low gradation) image with a wide dynamic range.
The Japanese Published Unexamined Patent Application No. S63-234269 discloses an image recording machine in which the gradation can be varied in a copy. The prior art image recording machine makes a copy of an original by performing the normal copying cycle twice. After the operator designates a part (or parts) of an original (e.g., a photograph part) where the gradation should be varied from the other part, the first copying cycle is performed. In the first copying cycle, the part of the drum surface corresponding to the designated part is discharged, and the copying conditions are adjusted to the text copying mode (i.e., the .gamma.-value is made large to obtain a low gradation image). The image on the drum is transferred to the copying sheet. Then the second copying cycle begins with the photograph copying mode (i.e., the .gamma.-value is made smaller to obtain a high gradation image). This time, the part of the drum corresponding to the text part (i.e., the part other than the designated part) is discharged. The prior art image recording machine uses an array of light emitting elements to discharge a part of the drum surface.
As easily seen, since the prior art image recording machine performs two copying cycles for a copy, it takes longer time to make a copy including a text part and a photograph part. Another problem of the prior art image recording machine is that the two images (text image and photograph image) transferred to a copying sheet can be displaced to each other.